Regarding the original Sega Mega Drive/Genesis release in 1991, three slight variations have been identified, the differences of which only a Sonic fan with a keen eye will be likely to spot. The original versions that hit the USA, Europe and Japan were all identical, though a revised version replaced it only in Japan at an unknown point in time. Version 2 famously features rather quick moving clouds in the Green Hill Zone and title screen, as opposed to stationary ones in the original, and the Labyrinth Zone received impressive rippling water effects in submerged portions of the level. The clouds in Marble Zone also operate under parallax scrolling and the stages in the level select cheat menu have been reorganised to the correct order. Because the original Japanese release occurred about a month after the US and Europe got it, others argue the first version of Sonic 1 never appeared in Japan, and they started with version 2, as that extra month allowed for these enhancements to be implemented. The truth is difficult to pin down. Version 3 also exists however, and was also only available in Japan after a certain point in time. This remains identical to version 2 except a common bug is fixed whereby if Sonic falls into a long pit of spikes, and then immediately back onto them again afterwards, he would continue to take damage without being able to recover. Version 3 is therefore the version of choice for Sonicists (or as I prefer, "Sonicians"), and Sonic Mega Collection supposedly contains all three versions buried in there somewhere.

This game has been ported or has made compilation appearances more often than any other Sonic game, and nowadays is available everywhere. Most are simply emulations that reproduce the game perfectly, but others make alterations according to what the hardware may allow, or for other reasons.

Possibly the most well known cheat for any game, ever. You should all know it off by heart, but just for the benefit of you young'uns... At the title screen, press up, down, left, then right. Upon hearing the chime of the ring sound effect, hold A and then press start and you'll be rewarded with the level select menu, where you can access any act of any zone, the final boss, Special Stage and the game's sound test. Essential. Use up and down to pick your option and A, B, C or start to begin. With Sound Test selected, use left and right to change the value and A, B, C or start to play the tune or sound effect associated with that value. Note that version 1 of the game has the levels in the wrong order. Versions 2 and 3 correct this (see Original Variations above to find out what the hell I'm talking about).

This is a secret mode intended for the use of the developers, to mess around with the object placements and move around the levels with the greatest of ease. Now, it can be yours, as they've left it in for a bit of fun. Similarly, at the title screen, press up, C, down, C, left, C, and right. You'll hear the ring chime. Hold down A and then press start, but keep A held down until Green Hill begins. If it worked correctly, you'll notice the score and time at the top is all buggered up, with strings of characters that indicate Sonic's position in the level. You can press B to turn Sonic into an object that appears in that zone. Move him around anywhere using the directional buttons, and press C to drop one of those objects in your current position. Press A to change the object and B again to return to your original hedgehog state. Whatever you plant only lasts for as long as you stay close to it though. If you leave the area a little way the stuff you placed will disappear, so you can't really customise the level particularly well, but it's good for getting to hidden locations and beating tough segments. Also, while he still takes damage, Sonic cannot die from hitting something without any rings, while in this mode.